1. Field of the Invention
The present invention generally relates to a plasma apparatus and, more particularly, to a plasma apparatus having an end-point detecting system utilizing an intensity variation of plasma light in a plasma process such as a plasma etching to a semiconductor wafer.
2. Description of the Related Art
In recent years, the high packing density and high integration of a semiconductor circuit device, typically, a dynamic random access memory (DRAM) are developing. Manufacturing of 16M bits DRAM is already stared and developing of 64M bits DRAM is prepared.
In the manufacturing process of such a semiconductor integration circuit device, micropatterning process technique plays an important role. Especially, plasma etching is employed as one of dry etching techniques. In the plasma etching technique, there is an apparatus based on the phenomenon that ions, molecules, or the like in a plasma generated by an electrical discharge in a low vacuum react with a substance (to be etched) to produce a volatile substance.
Such plasma etching process exhibits an excellent anisotropic etching effect in comparison with conventional wet etching, and hence is suitable for a micropatterning technique for forming grooves, each having a line width on the order of microns or less and a predetermined depth.
It is, therefore, very important for the manufacturing process of a semiconductor integration circuit device to detect an end-point of etching in plasma etching. As an apparatus for detecting an end-point of etching, an apparatus based on so-called emission spectrochemical analysis is generally used. In this apparatus, plasma light is converted into an electrical signal by a light-receiving element arranged at a transparent window portion of an etching chamber, and the electrical signal is monitored. That is, this analysis is performed by monitoring an intensity variation of light having a specific wavelength dependent on a volatile substance produced by etching.
More specifically, when plasma etching is started, a volatile substance is increased in amount, and a steady state is immediately set. However, as the etching process comes closer to an end, the volatile substance is decreased in amount, thus causing an intensity variation of light having a specific wavelength over time. An end-point is detected from this intensity variation.
For example, in a magnetron plasma etching apparatus as one of manufacturing apparatus of semiconductor integration circuit devices, a magnetic field is formed to cross an electric field formed between parallel electrodes for inducing a plasma discharge to obtain a high etching rate (about 1 .mu.m/min) thereby generating a plasma at a low pressure (about 10-3 norr).
As described above, detection of a plasma process end-point is indispensable to an etching apparatus of this type. For this reason, a transparent window portion is arranged on a process chamber in which a plasma is generated, and a plasma process end-point detecting apparatus (EPD) including a sensor for converting light having a specific wavelength into an electrical signal is arranged to oppose this window portion. The EPD detects the intensity of light having a specific wavelength during plasma emission, and detects a plasma process end-point when the intensity of the light having the specific wavelength is decreased to 60%, for example, provided that the intensity of the light is 100% in a steady state of the plasma process. In this case, since the time required for this detection is about 1 to 2 minutes, which is relatively long, a problem is posed in terms of error factors such as a variation.
In some magnetron plasma etching apparatus of this type, in order to improve etching characteristics, a magnet as a magnetic field forming means is rotated to form a uniform magnetic field so as to uniformity process in a surface of a wafer. In such an apparatus in which a plasma is generated in a rotating magnetic field, it is found that if a conventional EPD is directly applied to detection of a plasma process end-point, since a plasma is moved upon rotation of a magnetic field, a plasma process end-point cannot be accurately detected.
More specifically, since a plasma is moved upon rotation of a magnetic field, even if plasma process end-point detection is performed by detecting the intensity of light having a specific wavelength in the plasma by means of the EPD at a specific position, a detection timing may be offset. This is because the intensity variation of the plasma light is moved, and this variation is generally detected only once per rotation of the magnetic field.
Note that the above description is associated with a magnetron plasma etching apparatus. With regard to plasma process end-point detection in a normal plasma etching apparatus, the same problem as described above is posed. That is, accurate end-point detection information cannot be always obtained because of an uneven plasma light distribution.